Geoscience Reference
In-Depth Information
of studying blockage is discussed and results are presented. A simple blockage model is
described and its results are shown to agree with observations. Finally, examples of erroneous
wind measurements are shown and mitigation measures are discussed.
2. Background
2.1 Wind turbine development
Wind power technology dates back many centuries. In the 1st century A.D. Hero of
Alexandria described a simple wind wheel that could power an altar organ (Woodcroft, 1851).
It is, however, not clear whether this invention was ever constructed or put to use. The first
documented description of windmills that were used to perform irrigation and grinding grain
comes from the region of Sistan, Persia, in the 9th century (Shepard, 1990). By the 12th century
windmills were in use in Europe and in the following centuries they became increasingly
important for grinding grain and pumping water. It was only after the industrial revolution
their importance receded (Manwell et al., 2009).
Near the end of the 19th century the first wind turbines, used for the production of electricity,
were developed. James Blyth built a 10 m high, cloth-sailed wind turbine in Scotland in 1887
(Price, 2005) and Charles Brush constructed a 25 m high wind turbine in Cleveland, Ohio, in
1887-1888 (Anon., 1890). A few years later, in the 1890s, Poul la Cour constructed over 100
wind turbines to generate electricity in Denmark (Manwell et al., 2009). In the 1970s the rising
oil prices generated a renewed interest in wind power which led to serial production of wind
turbines.
The increasing demand for renewable energy sources in the 21st century led to a further
upswing for wind power. The pursuit of ever more powerful wind turbines lead to an
increase in rotor blade diameter. A large wind turbine in the early 1980s could have a rotor
diameter of 15 m and produce 55 kW whereas a large wind turbine in 2011 could have a rotor
diameter larger than 150 m and produce 7 MW. Figure 1 shows the rotor diameter and the
corresponding power produced by large wind turbines introduced on the market during the
period 1981-2011.
Since wind turbines not only have become increasingly powerful but also grown more
numerous during the last decades the global cumulative installed capacity has increased
exponentially (see Fig. 2). With the exception of year 2010 the global annual installed capacity
has increased monotonically since at least 1996 (cf. Fig. 2).
2.2 Wind turbine impact on Doppler radars
Wind turbines in the path of electromagnetic transmissions may cause interference by
scattering parts of the transmitted signal but also by modulating the transmission's frequency.
Initial studies on wind turbine interference focused on television and radio transmissions and
showed that wind turbines could indeed cause interference to the reception of such signals
(see, e.g., Sengupta (1984); Sengupta & Senior (1979); Senior et al. (1977); Wright & Eng (1992)).
By the end of the 20th century and beginning of the 21st century a large number of wind
turbines had been installed and several investigations were conducted to analyse the impact
of wind turbines on military surveillance radars and civilian air traffic control radars (see, e.g.,
